Influenza viruses of H5 and H7 types have caused heavy damage to the poultry industry mainly in Asia, and, in recent years, avian influenza virus was confirmed to be infectious also to human. In particular, in terms of avian influenza viruses belonging to H5 subtype, there are many reports as from 2003 on their infection to human and high lethality mainly in Asia, so that there is a worldwide concern of their pandemic due to absence of immunity against the viruses in human. Therefore, prophylaxis of, and countermeasures against them are being studied.
In order to prevent infection of avian influenza virus to human, or in order to prevent at least its outbreak in human, it is important to specifically and rapidly detect avian influenza virus that is infectious also to human. As a method for rapid detection of a virus in a sample, immunoassay has been conventionally widely used, and immunochromatography carried out by a sandwich immunoassay, wherein a solid phase in which an anti-virus antibody is immobilized on a part of a porous substrate through which a liquid is allowed to flow is used, has been especially widely used at clinical sites such as hospitals since viruses can be very simply detected in a short time thereby. Immunochromatography kits with which human influenza viruses can be detected are also commercially available.
In order to detect by immunoassay avian influenza virus that is also infectious to human, an antibody against the avian influenza virus is of course necessary. The surface antigens of influenza viruses are known to contain proteins called hemagglutinin and neuraminidase. As the hemagglutinin (HA), 16 types having different antigenicities, H1 to H16, are known, and, as the neuraminidase, 9 types having different antigenicities, N1 to N9, are known. The subtype of each influenza virus is represented by description of the types of these hemagglutinin and neuraminidase, such as “H5N1”. Most of the avian influenza viruses that have been so far confirmed to have been infected from bird to human are those having hemagglutinin of H5 type. Therefore, as an antibody to detect a highly pathogenic influenza virus that is infectious from bird to human, an antibody specific to H5 subtype influenza virus is demanded.
Hemagglutinin of H5 subtype influenza A virus has been studied well, and not only the amino acid sequence but also the spatial structure thereof are known (Non-patent Document 1). Further, various monoclonal antibodies against hemagglutinin of H5 subtype influenza A virus have been known (Non-patent Documents 2 to 4). Further, measurement of H5 subtype influenza A virus by a sandwich immunoassay using 2 types of hemagglutinin monoclonal antibodies has been known (Non-patent Documents 5 and 6).
[Non-patent Document 1] Ya Ha et al; The EMBO Journal, 21(5), 865-875, 2002
[Non-patent Document 2] Nikolai V. K. et al., J. Gen. Virol. 83, 2497, 2002
[Non-patent Document 3] James Stevens et al., SCIENCE VOL 312, 21 Apr. 2006
[Non-patent Document 4] Zhi-Yong Yang et al., SCIENCE VOL 317, 10 Aug. 2007
[Non-patent Document 5] Tsuda Y. et al., Microbiol. Immunol. 51(9), 903, 2007
[Non-patent Document 6] Qigai He et al., Clin. Vacc. Immunol. 617, 2007